Effects of Solids Retention Time on Extracellular Polymeric Substances (EPS) Recovery, Chain Length and Biodegradability

  • Paulo, A. (Main Examiner)
  • Daniela P. Mesquita (Supervisor)
  • M. Madalena Alves (Supervisor)
  • Victor Ajao (Supervisor)

Activity: Examination


Some industrial sectors produce wastewater that usually contains fine suspended solids and particles which can be problematic for the quality of water, to the aquatic life in general and soil contamination if they are discharged into the environment without proper treatment. The coagulation-flocculation process is a common method to solve this problem, however inorganic chemical coagulants and oil based synthetic flocculants are often used and they are harmful to the environment. Hence, it is becoming more important to replace these components with more sustainable natural bio-based flocculants. Microbial extracellular polymeric substances (EPS) are a new class of eco-safe flocculants that could be produced during the water treatment process.
In this work it was studied the effects of solids retention time (SRT), which is a reactor operational parameter, on the EPS production, chain length and biodegradability. Also, a study about the viability of fluorescence spectroscopy on EPS protein quantification was performed. The tested substance (EPS), on the first study, were produced with three membrane bioreactors operating at different SRTs (1d, 8d and 15d), each separately treating synthetic wastewater consisting in a carbon source (glycerol and ethanol) and a nutrients source (nitrogen). The reactors were operated under nitrogen-limited conditions (COD/N of 84.4) with influent COD of 922 mg/L. Under the mentioned conditions, high COD removal efficiencies of 81-96% were achieved. The reactor that achieved the highest total EPS concentration on the sludge line was SRT 8d, however the reactor with the highest S-EPS concentration and the most conversion of inlet COD into EPS was the reactor which operated with an SRT of 1d. Regarding the biodegradability assays, it was concluded that it might be possible the degradation of the produced EPS by their own producers under starving conditions.
The B-EPS that were submitted to 2D and 3D-EEM fluorescence spectroscopy analysis were produced on a sequence batch reactor with a synthetic medium containing mainly acetate and a trace elements solution. These measurements demonstrated promising results if the sample was simple, containing almost only protein. When the EPS samples were measured, the correlation were not so favourable, probably due to the complex matrix which compose the EPS.
Period20 Nov 2019
ExamineeAndré Wilson Novais Marques
Examination held at
  • University of Minho
Degree of RecognitionMaster